Gas chromatography is a standard technique in analytical chemistry for the separation of compounds in gaseous or vapour phase form, and the identification of components of such compounds.
FIG. 1 is a schematic diagram of a gas chromatograph.
As shown in FIG. 1, the gas chromatograph comprises a conduit 100, conventionally referred to as a column. This conduit 100 is provided with a column inlet 101, which itself receives a sample from sample inlet 110 and carrier inlet 120, passage through which is controlled by an inlet valve 121. At the opposite end of the conduit 100 is a column exhaust port 102. The exhaust port feeds into a chromatography detector 140 such as a flame ionisation detector or a thermal conductivity detector. The inside walls of the column 100 are lined with an adsorbent material 130. It will be appreciated that this figure is schematic in nature. In most cases, it will not be appropriate to provide a sample continuously, in which case an additional valve may be added to inlet 110. A three way valve may also be used to support selection between the carrier and the sample.
In operation, a gaseous or vapour phase sample is introduced through the sample inlet 110, and a flow of carrier gas introduced at a controlled velocity via carrier valve 121 causes the sample to be carried along the column 100. As it flows along the column, the sample will be exposed to the adsorbent material 130, which will have a varying affinity for different components of the sample, which will introduce a varying delay in the progress of different molecules along the column, depending on the composition of the adsorbent material, referred to as the eluotropic series of the adsorbent. At the exhaust port 130 the chromatography detector 140 continuously characterises the material arriving at the end of the conduit. By noting the timing of peaks in the detector readings with knowledge of the eluotropic series of the adsorbent 130, it is possible to determine the composition of the sample.
It is desired to develop gas chromatograph equipment offering improved sensitivity and capacity to discriminate between different gases.